This invention relates to apparatus capable of feeding marginally punched record material and, more particularly, to such an apparatus for use with a printing machine of the type comprising a platen and drive means for rotating the platen about its longitudinal axis.
When feeding marginally punched record material, such as computer forms paper, it is generally necessary to use a feeding apparatus different than the conventional platen-pressure roller arrangement, due to the thickness of the multi-copy paper and the use of periodic perforations for tearing purposes. The two most common feeding apparatus for this type of record material are the pin-feed apparatus and the tractor feed apparatus. An exemplary pin feed apparatus is disclosed in U.S. Pat. No. 4,033,493, whereas an exemplary tractor feed apparatus is disclosed in U.S. Pat. No. 4,042,091. In both the pin feed apparatus and the tractor feed apparatus, the platen pressure rollers must necessarily be disengaged during feeding by such apparatus. U.S. Pat. No. 4,042,091 discloses a novel manner by which this may be done automatically through movement of a guide rack included in the feed apparatus.
Very recently, it has become necessary to provide a record material feed apparatus with a bi-directional feeding capability. This is especially true when computer forms paper is used to print graphical data and the like. A pin feed apparatus having a bi-directional feeding capability is disclosed in U.S. Pat. No. 4,033,493. One problem with pin feed apparatus, however, is that the pin wheels are usually mounted on the platen drive shaft at the opposing ends of the platen. Thus, the size of the record material is normally restricted to a width substantially coincident with the length of the platen.
Tractor feed apparatus of the type disclosed in U.S. Pat. No. 4,042,091 avoid the above problem through the use of a pair of tractor feed assemblies slidably mounted on a pair of shafts adjacent to the platen. The slidability of these assemblies insures that virtually any sized record material up to the length of the platen itself can be employed. Tractor feed apparatus traditionally employ tractor feed assemblies of the above type each of which employes a continuous belt driven by pins projecting from the belt surface. The belt is driven by a single sprocket wheel mounted on one of the shafts to which the tractor feed assembly is slidably mounted.
In prior art bi-directional tractor feed apparatus using such tractor feed assemblies, one flat belt side is used to pull record material through the printer in one direction, and the other side of the same belt is used to pull it in the reverse direction. Loading of the record material in such apparatus is generally awkward and often results in damage to the marginally punched holes on the record material. It also usually requires either blind loading of the paper or requires that the apparatus be swivelable forwards to expose the reverse feeding side of the belt for loading. Additionally, sometimes the record material falls off the rear side of the tractor assemblies, if not properly supported, during operation. As another disadvantage, since the belt of each tractor assembly is driven by a single sprocket wheel, by a single shaft, and by one pair of drive gears, as is conventional, any free play in this extended mechanism results in a print position discrepancy between information printed after two different directions of drive.
It would be desirable, therefore, to provide a bi-directional record material feed apparatus that is easy to load with record material without pivoting the entire apparatus, and that can be reliably reversed in direction without adversly affecting print position alignment. It would further be desirable if such feed apparatus were of a type that does not restrict the size of record material to be fed, such as in the case of contempary tractor feed apparatus.